How can you prevent raw peaches from browning?

I am planning to make a Spanish hazelnut-chocolate cake that is topped with whipped cream and slices of raw peaches. When I made it before I added the peach slices just before serving, which was OK, but the peaches turned an ugly brown fairly quickly so the leftovers looked rather unappealing. I am thinking of adding some lemon juice or citric acid but I don't want to compromise the peach flavor. Any ideas?

For a cake, I'd try glazing the peaches with a thin layer of watered-down peach or apricot jelly. It's the type of glaze used to cover the tops of fruit tarts so the fruit won't brown. You basically heat up the jelly with water, about 2 parts water to 1 part jelly, then brush the heated (but not hot!) mixture over the fruit once it's on the tart. I haven't tried this on a cake before. I'm not sure whether it'd work better to dip the peach slices into the glaze first then set them on the cake, or to brush the glaze over the peach slices after they're on the cake. I suppose the danger with the latter is you'd get some glaze on the top of your cake and whipped cream. If it were me, I'd try dipping the slices and see how that worked. Your cake sounds delicious!

Another option would be to make a light glaze from jam (I like apricot) and just enough water to thin the jam when you heat them gently together -- then brush the peach slices gently with that: a French patisserie trick used for those lovely fruit tarts!